DECONTAMINATION
proteins is distorted because VeriTest Blue vials are cylindrical and create an optical effect of magnification.
Can a longer cycle with water only be as effective as one with the chemical?
Since that initial result was intriguing, we wondered whether those proteins would have been eventually cleaned with water only. To find out, we doubled the time of the main wash maintaining the same temperature profile. l Initial rinse: 2min at 25˚C lWash: - Stage 1: 10min at 42˚C - Stage 2: 10min at 55˚C
l No detergent was added l Rinse 1: 1min at 25˚C l Rinse 2: 1min at 25˚C
Picture 4 shows the result of that experiment. This time, tags were removed from the vials and photographed on a flat surface. Each tag still clearly shows a blue outline of proteins on the surface, confirming that blood and tissue contain an abundance of hydrophobic proteins that stick to surfaces very strongly.
Observations
Haemoglobin that gives blood its distinctive red colour is a protein that dissolves well in water and does not require complex cleaning chemistry to remove it from surfaces of PCDs and surgical instruments alike. What is left behind is very difficult to recognise by a naked eye. In our experiments, we had to set up photography spotlights in a specific way to highlight the layer of proteins because it was not clearly visible under regular light –
Picture 4. The blue residue of protein detecting dye on all four VeriTest AW tags.
be it artificial or daylight. Visual inspection of VeriTest Tags is much easier than regular surgical instruments as the contamination is initially applied to a flat and smooth surface that reflects the light in a consistent manner. Most surgical instruments have complex surfaces that are not flat and often not smooth. Moreover, with PCDs, we know precisely where to look for contamination, as we know where it was applied in the first place. With surgical instruments, contamination is randomly applied to the surfaces as they are used on the patients’ tissues. In addition, liquid blood can move on the surface of instruments and often penetrates the most sophisticated features of instruments, like joints and other very narrow gaps that are not directly visible without dismantling the instrument. VeriTest PCDs use a natural blend of blood and homogenised tissue to represent real
contamination accurately. Critically, they are composed of a mixture of water-soluble and insoluble proteins that replicate the behaviour of patients’ blood and tissue on instruments after surgery. The above examples show that with such a complex substance as natural test soil, we cannot merely rely on the absence of red colour to qualify something as clean and safe for reuse.
These results also show that good cleaning chemistry is required to clean the remaining “sticky” proteins off the surfaces. A well-optimised process was shown to remove contamination in a reasonably short time, and results were confirmed with a protein detecting dye.
CSJ
Reference 1. de Sternberg Stojalowski P. (2018) Cleaning of Hollow Instruments, verification and PCDs, IDI conference, Dublin.
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